A variety of metallocenes and other single site-like catalysts have been developed to prepare olefin polymers. Metallocenes are organometallic coordination complexes containing one or more π-bonded moieties (i.e., cyclopentadienyl groups) in association with a metal atom. Catalyst compositions containing metallocenes and other single site-like catalysts are highly useful for the preparation of polyolefins, producing relatively homogeneous copolymers at excellent polymerization rates while allowing one to closely tailor the final properties of the polymer as desired.
Recently, work relating to certain nitrogen-containing, single site-like catalyst precursors has been published. For example, WO 96/23101 relates to di(imine) metal complexes that are transition metal complexes of bidentate ligands selected from the group consisting of:
wherein said transition metal is selected from the group consisting of Ti, Zr, Sc, V, Cr, a rare earth metal, Fe, Co, Ni, and Pd;    R2 and R5 are each independently hydrocarbyl or substituted hydrocarbyl, provided that the carbon atom bound to the imino nitrogen atom has at least two carbon atoms bound to it;    R3 and R4 are each independently, hydrogen, hydrocarbyl, substituted hydrocarbyl, or R3 and R4 taken together are hydrocarbylene or substituted hydrocarbylene to form a carbocyclic ring;    R44 is a hydrocarbyl or substituted hydrocarbyl, and R28 is hydrogen, hydrocarbyl or substituted hydrocarbyl or R44 and R28 taken together form a ring;    R45 is a hydrocarbyl or substituted hydrocarbyl, and R29 is hydrogen, hydrocarbyl or substituted hydrocarbyl or R45 and R29 taken together form a ring;    each R30 is independently hydrogen, hydrocarbyl or substituted hydrocarbyl, or two of R30 taken together form a ring;    each R31 is independently hydrogen, hydrocarbyl or substituted hydrocarbyl;    R46 and R47 are each independently hydrocarbyl or substituted hydrocarbyl, provided that the carbon atom bound to the imino nitrogen atom has at least two carbon atoms bound to it;    R48 and R49 are each independently hydrogen, hydrocarbyl, or substituted hydrocarbyl;    R20 and R23 are each independently hydrocarbyl, or substituted hydrocarbyl;    R21 and R22 are independently hydrogen, hydrocarbyl, or substituted hydrocarbyl; and    n is 2 or 3;    and provided that:            the transition metal also has bonded to it a ligand that may be displaced by or added to the olefin monomer being polymerized; and            when the transition metal is Pd, said bidentate ligand is (V), (VII) or (VIII).
Also, U.S. Pat. No. 6,096,676 teaches a catalyst precursor having the formula:
wherein M is a Group IVB metal;    each L is a monovalent, bivalent, or trivalent anion;    X and Y are each heteroatoms, such as nitrogen;    each Cyclo is a cyclic moiety;    each R1 is a group containing 1 to 50 atoms selected from the group consisting of hydrogen and Group IIIA to Group VIIA elements, and two or more adjacent R1 groups may be joined to form a cyclic moiety;    each R2 is a group containing 1 to 50 atoms selected from the group consisting of hydrogen and Group IIIA to Group VIIA elements and two or more adjacent R2 groups may be joined to form a cyclic moiety;    W is a bridging group; and    each m is independently an integer from 0 to 5.Also taught is a catalyst composition comprising this catalyst precursor and an activating co-catalyst, as well as a process for the polymerization of olefins using this catalyst composition.
Although there are a variety of single site catalysts taught in the art, some of which are commercially available, there still exist a need for improved catalysts and catalyst precursors that are capable of producing polyolefins having predetermined properties.